LHC Machine Protection

1

LHC Machine LHC Machine ProtectionProtection

Acknowledgments to my colleagues of the MPWG Rossano Rossano GiachinoGiachino for input and material. J.Wenninger B.Todd R.Schmidt B. Puccio September 2007

OutlineOutline

• Energy stored in the LHC magnets• LHC Dipole Magnets• Power Interlock Controllers• Quench Protection System

• Energy stored in the LHC beams • LHC Beam Energy• Beam Losses and Damage Potential• Beam Absorbers, Beam Dump and Collimators• Beam Interlock System

• Conclusion

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Beam 1

3

Top energy/GeV Circumference/m Linac 0.12 30PSB 1.4 157CPS 26 628 = 4 PSBSPS 450 6’911 = 11 x PSLHC 7000 26’657 = 27/7 xSPS

LEIR

CPS

SPS

Booster

LINACS

LHC

3

45

6

7

8

1

2

Ions

protons

Beam 1

Beam 2

TI8

TI2

Note the energy gain/machine of 10 to 20 – and not more !

The gain is typical for the useful range of magnets !!!

4

Sector

1

5

DC Power feed

3

Oct

ant

DC Power

2

4 6

8

7LHC27 km Circumference

Powering Sector:

154 dipole magnets &about 50 quadrupolestotal length of 2.9 km

LHC Powering in 8 Sectors

Powering Subsectors:

• long arc cryostats• triplet cryostats• cryostats in matching section

0

2000

4000

6000

8000

10000

12000

-4000 -2000 0 2000 4000

time from start of injection (s)

dip

ole

cu

rre

nt (A

)

energy

ramp

preparation and access

beam dump

injection phase

coast

coast

LHC cycle: charging the magnetic energyLHC cycle: charging the magnetic energy

L.Bottura

450 GeV

7 TeV

start of the

ramp

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OutlineOutline



• Conclusion

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Energy stored in LHC magnets : whereEnergy stored in LHC magnets : whereMost energy is stored in the magnetic field of the

dipoles

B = 8.33 Tesla I = 11800 A L = 0.108 H

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Energy stored in LHC magnets Energy stored in LHC magnets

Energy is proportional to volume inside magnet aperture and to the square of the magnet field

E dipole = 0.5 L dipole I 2dipole

Energy stored in one dipole is 7.6 MJoule

For all 1232 dipoles in the LHC: 9.4 GJ

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The energy stored in the magnets corresponds The energy stored in the magnets corresponds to ..to ..

an aircraft carrier at battle-speed of 55 km/han aircraft carrier at battle-speed of 55 km/h

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The energy stored in the magnets corresponds The energy stored in the magnets corresponds to ..to ..

An important point to determine :

How fast can this energy be released?

10 GJoule corresponds to…

the energy of 1900 kg TNTthe energy of 400 kg Chocolate

Powering Interlock ControllerPowering Interlock Controller

• PLC-based Powering Interlock Controllers (PIC) are used to manage the interlock signal between the power converters and the quench protection system.

• The PIC also interfaces to the Beam Interlock System and will request a beam dump if the electrical circuit that fails is considered to be critical for beam operation.

Powering Interlock System

Quench Protection

Power Converters

Discharge Switches

AUG

UPS

Cryogenics

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QuenchQuench

A Quench is the phase transition of a super-conducting to a normal conducting state.

Quenches are initiated by an energy in the order of mJ• Movement of the superconductor by several m (friction and

heat dissipation)• Beam losses• Failure in cooling

To limit the temperature increase after a quench• The quench has to be detected• The energy is distributed in the magnet by force-quenching the

coils using quench heaters• The magnet current has to be switched off within << 1 second

Energy extraction system in LHC Energy extraction system in LHC tunneltunnel

Resistors absorbing the energy

Switches - for switching the resistors into series with the magnets

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If it does not work…If it does not work…

P.Pugnat

During magnet testing the 7 MJ stored in one magnet were released into one spot of the coil (inter-turn short)

Challenges for quench protectionChallenges for quench protection

• Detection of quench for all main magnets • 1600 magnets in 24 electrical circuits• ~800 others

• Detection of quench across all HTS current leads• 2000 Current Leads

• Firing heater power supplies, about • 6000 heater units

Failure in protection system

False quench detection: downtime of some hoursMissed quench detection: damage of magnet, downtime

30 days

Systems must be very reliable

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OutlineOutline



• Conclusion

Energy stored in the beamsEnergy stored in the beams

Stored beam energy: Proton Energy Number of Bunches Number of protons per

bunch

Proton Energy: 7 TeV

In order to achieve very high luminosity:

Number of bunches per beam: 2808

Number of protons per bunch: 1.05 ×1011

Stored energy per beam: 362 MJoule

25 ns

3×1014 protons / beam

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Stored energy comparisonStored energy comparison

0.01

0.10

1.00

10.00

100.00

1000.00

10000.00

1 10 100 1000 10000Momentum [GeV/c]

En

erg

y s

tore

d in

th

e b

ea

m [

MJ

]

LHC topenergy

LHC injection(12 SPS batches)

ISR

SNSLEP2

SPS fixed target HERA

TEVATRON

SPSppbar

SPS batch to LHC

Factor~200

RHIC proton

LHC energy in magnets

Increase with respect to existing accelerators :

•A factor 2 in magnetic field

•A factor 7 in beam energy

•A factor 200 in stored energy

A proton injected into the LHC will end its A proton injected into the LHC will end its life…life…

• In a collision with an opposing beam proton• The goal of the LHC !

• On the LHC beam dump• At the end of a fill, be it scheduled or not.

• On a collimator or on a protection device/absorber• The collimators must absorb protons that wander off

to large amplitudes to avoid quenches.

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Beam induced damage testBeam induced damage test

25 cm

Controlled experiment: Special target (sandwich of Tin, Steel, Copper plates)

installed in an SPS transfer line. Impact of 450 GeV LHC beam (beam size σx/y ~ 1 mm)

Beam

The effect of a high intensity beam impacting on equipment is not so easy to evaluate, in particular when you are looking for damage :

heating, melting, vaporization …

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Results….Results….

A B D C

Shot Intensity / p+

A 1.2×1012

B 2.4×1012

C 4.8×1012

D 7.2×1012

• Melting point of Copper is reached for an impact of 2.5×1012 p.

• Stainless steel is not damaged, even with 7×1012 p.

• Results agree with simulation

Based on those results the MPWG has adopted for the LHC a limit for safe beams with nominal emittance @ 450 GeV of:

1012 protons ~ 0.3% of the total intensity

Scaling the results yields a limit @ 7 TeV of:

1010 protons ~ 0.003% of the total intensity

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Beam absorberBeam absorber

• The beam dump block is the ONLY element of the LHC that can safely absorb all the beam!

• All other absorbers in the LHC (collimators and protection devices) can only stand partial losses – typically up to a full injected beam, i.e. equivalent to the energy stored in the SPS at 450 GeV.

Beam Energy Tracking

Beam Dumping System

DCCT Dipole Current 1


RF turn clock

LHC Layout

IR3, IR6 and IR7 are devoted to protection and collimation ! IR6: Beam

dumping systemIR4: Radio frequency

acceleration

IR5:CMSexperiment

IR1: ATLASexperiment

IR8: LHC-BexperimentIR2: ALICE

experiment

InjectionInjection

IR3: Momentum Collimation (normal

conducting magnets)

IR7: Collimation (normal conducting magnets)

Beam dump blocks

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LHC Layout

IR3, IR6 and IR7 are devoted to protection and collimation ! IR6: Beam

dumping systemIR4: Radio frequency

acceleration

IR5:CMSexperiment

IR1: ATLASexperiment

IR8: LHC-BexperimentIR2: ALICE

experiment

InjectionInjection

IR3: Momentum Collimation (normal

conducting magnets)

IR7: Collimation (normal conducting magnets)

Beam dump blocks

about 8 m

concrete shielding

beam absorber (graphite)

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Beam +/- 3 sigma

56.0 mm

1 mm

+/- 6 sigma = 3.0 mm

Example: Setting of collimators at 7 TeV - with luminosity opticsExample: Setting of collimators at 7 TeV - with luminosity optics Very tight settings Very tight settings orbit feedback !! orbit feedback !!

Ralphs Assmanns EURO

Collimators at Collimators at 7 TeV, 7 TeV, squeezedsqueezedopticsoptics

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Beam Interlock System and InputsBeam Interlock System and Inputs• Protection for the entire machine against

beam incidents.• Interface to all parties involved in

protection, including powering interlock systems and injectors (SPS).

• Microsecond reaction times.

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Injection Kickers

Safe LHCParameters

Beam Current Monitors Current

EnergyEnergy

SafeBeamFlag

Energy SPS ExtractionInterlocks

TL collimators


Beam Dumping System



RF turn clock

LHCBeam

Interlock System

Access Safety System

Beam DumpTrigger

Timing PM Trigger

BLMs aperture

BPMs for Beam Dump

LHC Experiments

Collimators / Absorbers

NC Magnet Interlocks

Vacuum System

RF + Damper

dI/dt beam current

BLMs arc

BPMs for dx/dt + dy/dt

dI/dt magnet current

OperatorsSoftware Interlocks

Screens


Quench Protection

Power Converters

Discharge Switches

AUG

UPS

Cryogenics essentialcircuits

auxiliarycircuits

Beam Interlock System and InputsBeam Interlock System and Inputs• Protection for the entire machine against

beam incidents.• Interface to all parties involved in

protection, including powering interlock systems and injectors (SPS).

• Microsecond reaction times.

ArchitectureArchitecture of the BEAM INTERLOCK SYSTEM of the BEAM INTERLOCK SYSTEM

Beam-1 / Beam-2 are Independent!

20 Users per BICHalf maskable

Half un-maskable

- fast reaction time (~ s)

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Safe LHC parametersSafe LHC parameters

Safe Beam Flags required by• Beam Interlock Controllers, to permit masking of selected

interlock channels, in particular during commissioning• Aperture kickers, to disable kickers when there is no

“safe” beam

Beam Presence Flags required by• SPS extraction, to permit extraction of high intensity

beam only when there is circulating beam in the LHC

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Machine protection systems

LHCBeam

Interlock System


BLMs aperture

BPMs for Beam Dump

LHC Experiments

Collimators / Absorbers

NC Magnet Interlocks

Vacuum System

RF + Damper


Access Safety System

Quench Protection

Power Converters

Discharge Switches

dI/dt beam current

Beam Dumping System

AUG

UPS



RF turn clock

Cryogenics

Beam DumpTrigger

Beam Current Monitors Current

BLMs arc

BPMs for dx/dt + dy/dt

dI/dt magnet current

Energy

SPS ExtractionInterlocks

Injection Kickers

Safe LHCParametersEnergy

Timing

essentialcircuits

auxiliarycircuits Screens

SafeBeamFlag

Energy

TL collimators

Software Interlocks

Green : ready before first beam

Software Interlocks

Operators

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OutlineOutline



• Conclusion

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ConclusionsConclusionsThere is no single “Machine Protection System”: LHC Machine

Protection relies on several systems working reliably together

Safe operation of the LHC start at the SPS, via extraction into TT40/TI8 and TI2, via the transfer lines, via LHC injection etc.

Safe operation of the LHC requires a culture:• as soon as the magnets are powered, there is the risk of damage due

to the stored magnet energy• as soon as the beam intensity is above a certain value (…that is much

less than 0.1% of the full 7 TeV beam), there is the risk of beam induced damage

• safe operation of the LHC relies not only on the various hardware systems, but also on operational procedures and on the controls system (“software interlocks”)

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Machine protection at the LHCMachine protection at the LHC

• Machine protection activities of the LHC are coordinated by the LHC Machine Protection Working Group (MPWG), co-chaired by R. Schmidt & J. Wenninger.http://lhc-mpwg.web.cern.ch/lhc-mpwg/

• Since 2004 the MPWG is also coordinating machine protection at the SPS (ring & transfer lines).

http://lhc-mpwg.web.cern.ch/lhc-mpwg/

http://lhc-mpwg.web.cern.ch/lhc-mpwg/

Documents

LHC Machine Protection